8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and on reverse ratio. The transmission includes four planetary gear sets, five torque-transmitting devices, three fixed interconnections and a grounded member. The powertrain includes an engine and torque converter that is continuously connected to one of the planetary gear members. The five torque-transmitting devices provide interconnections between various gear members, and the transmission housing, and are operated in combinations of two to establish eight forward speed ratios and on reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having fourplanetary gear sets that are controlled by five torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvedtransmission having four planetary gear sets controlled to provide eightforward speed ratios and one reverse speed ratio.

The transmission family of the present invention has four planetary gearsets, each of which includes a first, second and third member, whichmembers may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second, third and fourth gear sets in thisdescription and in the claims, these sets may be counted “first” to“fourth” in any order in the drawing (i.e., left to right, right toleft, etc.). Additionally, the first, second or third members of eachgear set may be counted “first” to “third” in any order in the drawing(i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the second memberof the first planetary gear set with the third member of the secondplanetary gear set and with the third member of the third planetary gearset.

A second interconnecting member continuously connects the first memberof the third planetary gear set with the first member of the fourthplanetary gear set.

A third interconnecting member continuously connects the first member ofthe second planetary gear set with the second member of the fourthplanetary gear set.

The input member is continuously connected with the first member of thesecond planetary gear set. The output member is continuously connectedwith the third member of the fourth planetary gear set. The third memberof the first planetary gear set is continuously connected with astationary member.

A first torque-transmitting device, such as a brake, selectivelyconnects the second member of the third planetary gear set with astationary member (transmission housing/casing).

A second torque-transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with the firstmember of the second planetary gear set.

A third torque-transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with thesecond member of the second planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the first planetary gear set with thesecond member of the third planetary gear set.

A fifth torque-transmitting device, such as a clutch, selectivelyconnects the second member of the second planetary gear set with thethird member of the fourth planetary gear set.

The five torque-transmitting devices are selectively engageable incombinations of two to yield eight forward speed ratios and one reversespeed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes four planetary gear sets20, 30, 40 and 50.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the ring gear member 24 and the sun gear member 22.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 rotatablymounted on a carrier member 39 and disposed in meshing relationship withboth the sun gear member 32 and the ring gear member 34.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47, 48 mountedon a carrier member 49. The pinion gears 47 are disposed in meshingrelationship with the sun gear member 42, and the pinion gears 48 aredisposed in meshing relationship with both the ring gear member 44 andthe respective pinion gear 47.

The planetary gear set 50 includes a sun gear member 52, a ring gearmember 54, and a planet carrier assembly member 56. The planet carrierassembly member 56 includes a plurality of pinion gears 57 mounted on acarrier member 59 and disposed in meshing relationship with both the sungear member 52 and the ring gear member 54.

The planetary gear arrangement also includes five torque-transmittingdevices 80, 82, 84, 85 and 86. The torque-transmitting device 80 is astationary-type torque-transmitting device, commonly termed brake orreaction clutch. The torque-transmitting devices 82, 84, 85 and 86 arerotating-type torque-transmitting devices, commonly termed clutches.

The input member 17 is continuously connected with the planet carrierassembly member 56 of the planetary gear set 50 and the sun gear member32 of the planetary gear set 30. The output member 19 is continuouslyconnected with the ring gear member 54 of the planetary gear set 50. Thering gear member 24 of the planetary gear set 20 is continuouslyconnected with the transmission housing 60.

A first interconnecting member 70 continuously connects the planetcarrier assembly member 26 of the planetary gear set 20 with the ringgear member 34 of the planetary gear set 30 and with the ring gearmember 44 of the planetary gear set 40. A second interconnecting member72 continuously connects the sun gear member 42 of the planetary gearset 40 with the sun gear member 52 of the planetary gear set 50. A thirdinterconnecting member 74 continuously connects the sun gear member 32of the planetary gear set 30 with the planet carrier assembly member 56of the planetary gear set 50.

A first torque-transmitting device, such as brake 80, selectivelyconnects the planet carrier assembly member 46 of the planetary gear set40 with the transmission housing 60. A second torque-transmittingdevice, such as clutch 82, selectively connects the sun gear member 22of the planetary gear set 20 with the sun gear member 32 of theplanetary gear set 30 and planet carrier assembly member 56 of theplanetary gear set 50 via interconnecting member 74. A thirdtorque-transmitting device, such as clutch 84, selectively connects thesun gear member 22 of the planetary gear set 20 with the planet carrierassembly member 36 of the planetary gear set 30. A fourthtorque-transmitting device, such as clutch 85, selectively connects thesun gear member 22 of the planetary gear set 20 with the planet carrierassembly member 46 of the planetary gear set 40. A fifthtorque-transmitting device, such as clutch 86, selectively connects theplanet carrier assembly member 36 of the planetary gear set 30 with thering gear member 54 of the planetary gear set 50.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of two to provide eight forward speed ratios and onereverse speed ratio, all with single transition sequential shifts andfour overdrive ratios.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.53, while the step ratio between the reversespeed ratio and first forward ratio is −0.78.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Further explanation of the format, purpose and use of lever diagrams canbe found in SAE Paper 810102, authored by Benford, Howard and Leising,Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981,which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, an output member 19 continuously connected with thefinal drive mechanism 16, a first planetary gear set 20A having threenodes: a first node 22A, a second node 26A and a third node 24A; asecond planetary gear set 30A having three nodes: a first node 32A, asecond node 36A and a third node 34A; a third planetary gear set 40Ahaving three nodes: a first node 42A, a second node 46A and a third node44A; and a fourth planetary gear set 50A having three nodes: a firstnode 52A, a second node 56A and a third node 54A.

The input member 17 is continuously connected with the nodes 32A and56A. The output member 19 is continuously connected with the node 54A.The node 24A is continuously connected with the transmission housing 60.

The nodes 26A, 34A and 44A are continuously connected viainterconnecting member 70. The node 42A is continuously connected withnode 52A via interconnecting member 72. The node 32A is continuouslyconnected with node 56A via interconnecting member 74.

A first torque-transmitting device, such as brake 80, selectivelyconnects the node 46A with the transmission housing 60. A secondtorque-transmitting device, such as clutch 82, selectively connects thenode 22A with the nodes 32A and 56A via interconnecting member 74. Athird torque-transmitting device, such as clutch 84, selectivelyconnects the node 22A with the node 36A. A fourth torque-transmittingdevice, such as clutch 85, selectively connects the node 22A with thenode 46A. A fifth torque-transmitting device, such as clutch 86,selectively connects the node 36A with the node 54A.

To establish ratios, two torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row of FIG. 1 b. For example, to establishreverse gear, the clutches 85 and 86 are engaged. The clutch 85 engagesthe node 22A with the node 46A. The clutch 86 engages the node 36A withthe node 54A. Likewise, the eight forward ratios are achieved throughdifferent combinations of clutch engagement as per FIG. 1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havingfirst, second and third members; said third member of said firstplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidsecond member of said first planetary gear set with said third member ofsaid second planetary gear set and with said third member of said thirdplanetary gear set; a second interconnecting member continuouslyconnecting said first member of said third planetary gear set with saidfirst member of said fourth planetary gear set; a third interconnectingmember continuously connecting said first member of said secondplanetary gear set with said second member of said fourth planetary gearset; and five torque-transmitting devices for selectivelyinterconnecting said members of said planetary gear sets with saidstationary member or with other members of said planetary gear sets,said five torque-transmitting devices being engaged in combinations oftwo to establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member. 2.The transmission of claim 1, wherein a first of said fivetorque-transmitting devices is operable for selectively connecting saidsecond member of said third planetary gear set with said stationarymember.
 3. The transmission of claim 2, wherein a second of said fivetorque-transmitting devices is operable for selectively connecting saidfirst member of said first planetary gear set with said first member ofsaid second planetary gear set.
 4. The transmission of claim 3, whereina third of said five torque-transmitting devices is operable forselectively connecting said first member of said first planetary gearset with said second member of said second planetary gear set.
 5. Thetransmission of claim 4, wherein a fourth of said fivetorque-transmitting devices is operable for selectively connecting saidfirst member of said first planetary gear set with said second member ofsaid third planetary gear set.
 6. The transmission of claim 5, wherein afifth of said five torque-transmitting devices is operable forselectively connecting said second member of said second planetary gearset with said third member of said fourth planetary gear set.
 7. Thetransmission defined in claim 1, wherein a first of said fivetorque-transmitting devices comprises a brake, and a second, third,fourth and fifth of said five torque-transmitting devices compriseclutches.
 8. The transmission of claim 1, wherein said first, second andthird members of said first, second, third and fourth planetary gearsets comprise a sun gear member, a planet carrier assembly member and aring gear member, respectively.
 9. The transmission of claim 1, whereinsaid input member is continuously connected with said first member ofsaid second planetary gear set, and said output member is continuouslyconnected with said third member of said fourth planetary gear set. 10.A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havingfirst, second and third members; said input member being continuouslyconnected with said first member of said second planetary gear set; andsaid output member being continuously connected with said third memberof said fourth planetary gear set; said third member of said firstplanetary gear set being continuously connected with a stationarymember; a first interconnecting member continuously connecting saidsecond member of said first planetary gear set with said third member ofsaid second planetary gear set and with said third member of said thirdplanetary gear set; a second interconnecting member continuouslyconnecting said first member of said third planetary gear set with saidfirst member of said fourth planetary gear set; a third interconnectingmember continuously connecting said first member of said secondplanetary gear set with said second member of said fourth planetary gearset; a first torque-transmitting device selectively connecting saidsecond member of said third planetary gear set with the stationarymember; a second torque-transmitting device selectively connecting saidfirst member of said first planetary gear set with said first member ofsaid second planetary gear set; a third torque-transmitting deviceselectively connecting said first member of said first planetary gearset with said second member of said second planetary gear set; a fourthtorque-transmitting device selectively connecting said first member ofsaid first planetary gear set with said second member of said thirdplanetary gear set; a fifth torque-transmitting device selectivelyconnecting said second member of said second planetary gear set withsaid third member of said fourth planetary gear set; and said fivetorque-transmitting devices being engaged in combinations of two toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.
 11. Thetransmission of claim 10, wherein said first, second and third membersof said first, second, third and fourth planetary gear sets comprise asun gear member, a planet carrier assembly member and a ring gearmember, respectively.
 12. A multi-speed transmission comprising: aninput member; an output member; first, second, third and fourthplanetary gear sets each having a sun gear member, planet carrierassembly member and ring gear member; said input member beingcontinuously interconnected with said sun gear member of said secondplanetary gear set; and said output member being continuouslyinterconnected with said ring gear member of said fourth planetary gearset; said ring gear member of said first planetary gear set beingcontinuously connected with a stationary member; a first interconnectingmember continuously connecting said planet carrier assembly member ofsaid first planetary gear set with said ring gear member of said secondplanetary gear set and with said ring gear member of said thirdplanetary gear set; a second interconnecting member continuouslyconnecting said sun gear member of said third planetary gear set withsaid sun gear member of said fourth planetary gear set; a thirdinterconnecting member continuously connecting said sun gear member ofsaid second planetary gear set with said planet carrier assembly memberof said fourth planetary gear set; a first torque-transmitting deviceselectively connecting said planet carrier assembly member of said thirdplanetary gear set with the stationary member; a secondtorque-transmitting device selectively connecting said sun gear memberof said first planetary gear set with said sun gear member of saidsecond planetary gear set; a third torque-transmitting deviceselectively connecting said sun gear member of said first planetary gearset with said planet carrier assembly member of said second planetarygear set; a fourth torque-transmitting device selectively connectingsaid sun gear member of said first planetary gear set with said planetcarrier assembly member of said third planetary gear set; a fifthtorque-transmitting device selectively connecting said planet carrierassembly member of said second planetary gear set with said ring gearmember of said fourth planetary gear set; and said fivetorque-transmitting devices being engaged in combinations of two toestablish eight forward speed ratios and one reverse speed ratio betweensaid input member and said output member.